Large Resistance Change Research Articles

ChemInform Abstract: CPP Magnetoresistance of Magnetic Multilayers: A Critical Review

AbstractReview: 380 refs.

High sensitivity sensor development for Hexamethylphosphoramide by polyaniline coated polyurethane membrane using resistivity assessment technique

Hexamethylphosphoramide is considered as one of the harmful of all carcinogens. In the present work, detection of Hexamethylphosphoramide by using a polyaniline coated polyurethane membrane was carried out and device is constructed to show its practical application using resistivity assessment technique. Polyurethane nanofiber membrane was prepared by electrospinning process. A modified synthetic method used to coat polyaniline onto a polyurethane membrane found to be effective to prepare a uniform and electrically conductive coating and promising for sensing a carcinogen like Hexamethylphosphoramide. Sensing performance may be attributed to the large resistance change in polyaniline because of the deprotonation when exposed to the Hexamethylphosphoramide environment. However, it is interesting to know that the high sensitivity of polyaniline modified polyurethane membrane toward Hexamethylphosphoramide is used as a promising gas sensor for the detection of said carcinogen using resistivity assessment technique at room temperature.

Spin-torque resonant expulsion of the vortex core for an efficient radiofrequency detection scheme.

It has been proposed that high-frequency detectors based on the so-called spin-torque diode effect in spin transfer oscillators could eventually replace conventional Schottky diodes due to their nanoscale size, frequency tunability and large output sensitivity. Although a promising candidate for information and communications technology applications, the output voltage generated from this effect has still to be improved and, more pertinently, reduces drastically with decreasing radiofrequency (RF) current. Here we present a scheme for a new type of spintronics-based high-frequency detector based on the expulsion of the vortex core in a magnetic tunnel junction (MTJ). The resonant expulsion of the core leads to a large and sharp change in resistance associated with the difference in magnetoresistance between the vortex ground state and the final C-state configuration. Interestingly, this reversible effect is independent of the incoming RF current amplitude, offering a fast real-time RF threshold detector.

Gas sensing behavior of electrospun nickel oxide nanofibers: Effect of morphology and microstructure

Metal oxide nanofibers are promising candidates for gas sensing applications due to their high surface area, pseudo one-dimensional structure and semi-conducting characteristics. The sensitivity of metal oxide nanofibers to different gases can be further maximized by controlling their morphology and microstructure. In this context, nickel oxide nanofibers were synthesized with controlled morphology and microstructure through the electrospinning technique using a solution composed of nickel acetate salt and poly(vinyl alcohol) polymer followed by calcination and annealing. These nanofibers were then employed as hydrogen and ammonia sensors. The diameter and crystallinity of the nanofibers increased, whereas the surface area decreased, with increasing ratio of salt to polymer in the solution. Nanofibers with intermediate diameter, crystallinity and surface area were found to undergo the largest resistance changes when exposed to hydrogen and ammonia at elevated temperatures. Furthermore, we found that appropriate annealing of these nickel oxide nanofibers led to full crystallinity, with a drastic increase in crystallite size and several fold decrease in surface area. These fully crystalline nanofibers possessed much lower sensitivity to hydrogen and ammonia but faster recovery as compared to their semicrystalline counterparts. In addition to surface area variations, different dominant sensing mechanisms are proposed to explain the observed differences in sensing behavior.

Ultraflexible, large-area, physiological temperature sensors for multipoint measurements

We report a fabrication method for flexible and printable thermal sensors based on composites of semicrystalline acrylate polymers and graphite with a high sensitivity of 20 mK and a high-speed response time of less than 100 ms. These devices exhibit large resistance changes near body temperature under physiological conditions with high repeatability (1,800 times). Device performance is largely unaffected by bending to radii below 700 µm, which allows for conformal application to the surface of living tissue. The sensing temperature can be tuned between 25 °C and 50 °C, which covers all relevant physiological temperatures. Furthermore, we demonstrate flexible active-matrix thermal sensors which can resolve spatial temperature gradients over a large area. With this flexible ultrasensitive temperature sensor we succeeded in the in vivo measurement of cyclic temperatures changes of 0.1 °C in a rat lung during breathing, without interference from constant tissue motion. This result conclusively shows that the lung of a warm-blooded animal maintains surprising temperature stability despite the large difference between core temperature and inhaled air temperature.

Probabilistic 3-D time-lapse inversion of magnetotelluric data: application to an enhanced geothermal system

SUMMARY Surface-based monitoring of mass transfer caused by injections and extractions in deep boreholes is crucial to maximize oil, gas and geothermal production. Inductive electromagnetic methods, such as magnetotellurics, are appealing for these applications due to their large penetration depths and sensitivity to changes in fluid conductivity and fracture connectivity. In this work, we propose a 3-D Markov chain Monte Carlo inversion of time-lapse magnetotelluric data to image mass transfer following a saline fluid injection. The inversion estimates the posterior probability density function of the resulting plume, and thereby quantifies model uncertainty. To decrease computation times, we base the parametrization on a reduced Legendre moment decomposition of the plume. A synthetic test shows that our methodology is effective when the electrical resistivity structure prior to the injection is well known. The centre of mass and spread of the plume are well retrieved. We then apply our inversion strategy to an injection experiment in an enhanced geothermal system at Paralana, South Australia, and compare it to a 3-D deterministic time-lapse inversion. The latter retrieves resistivity changes that are more shallow than the actual injection interval, whereas the probabilistic inversion retrieves plumes that are located at the correct depths and oriented in a preferential north–south direction. To explain the time-lapse data, the inversion requires unrealistically large resistivity changes with respect to the base model. We suggest that this is partly explained by unaccounted subsurface heterogeneities in the base model from which time-lapse changes are inferred.

Self-Assembling VO2 Nanonet with High Switching Performance at Wafer-Scale

Technologically controlling nanostructures is essential to tailoring the functionalities and properties of nanomaterials. Various methods free from lithography-based techniques have been employed to fabricate 2D nanostructures; however it is still hard to achieve a well interconnected 2D regular nanostructure. Here, we demonstrate a facile chemical solution method to self-assemble a regular and interconnected VO2 nanonet on the wafer scale. The nanonet shows a well-defined 2D truss network constructed by VO2 nanorods with twinning relationships. The growth direction and crystallographic orientation of nanorods are synchronously controlled, leading to horizontally epitaxial growth of nanorods along three symmetric directions of the (001) single-crystal sapphire substrate. The unique nanonets enable the acquisition of excellent resistance switching properties and dramatic fatigue endurance. A large resistance change of near 5 orders with a 1.7 °C width of the hysteresis loop is characterized comparably to t...

For progress in natural science: Materials international investigations of structural phase transformation and THz properties across metal–insulator transition in VO2/Al2O3 epitaxial films

Vanadium dioxide (VO2) epitaxial thin films on (0001)-oriented Al2O3 substrates were prepared using radio frequency (RF) magnetron sputtering techniques. To study the metal-insulator-transition (MIT) mechanism and extend the applications of VO2 epitaxial films at terahertz (THz) band, temperature-dependent X-ray diffraction (XRD) and THz time domain spectroscopy of the VO2 epitaxial films were performed. Both the lattice constants and THz transmission exhibited a similar and sharp transition that was similar to that observed for the electrical resistance. Consequently, the MIT of the VO2/Al2O3 epitaxial films should be co-triggered by the structural phase transition and electronic transition. Moreover, the very large resistance change (on the order of ~103) and THz response (with a transmission modulation ratio of ~87%) in the VO2/Al2O3 epitaxial heterostructures are promising for electrical switch and electro-optical device applications.

Magnetically modulated laser-induced resistance effect observed in Metal-Oxide-Semiconductor structure of Cr/SiO(2)/Si.

In this study, we report our finding of laser-induced resistance effect in metal-oxide-semiconductor (MOS) structure of Cr/SiO(2)/Si. Under the irradiation of a laser beam, the effect shows a large linear resistance change ratio of 92% with a spatial sensitivity of 0.79 MΩ/mm. In particular, by the application of an external magnetic field perpendicular to the Cr film, the resistance change ratio is increased to 110%. This effect is attributed to the Lorentz force acting on the photo-generated carriers in the inversion layer of MOS structures. The work suggests an approach for the development of new type magnetically modulated photoelectric devices.

Giant magnetoelectric coupling interaction in BaTiO3/BiFeO3/BaTiO3 trilayer multiferroic heterostructures

Multiferroic trilayer thin films of BaTiO3/BiFeO3/BaTiO3 were prepared by RF-magnetron sputtering technique at different thicknesses of BiFeO3 layer. A pure phase polycrystalline growth of thin films was confirmed from X-ray diffraction results. The film showed maximum remnant electric polarization (2Pr) of 13.5 μC/cm2 and saturation magnetization (Ms) of 61 emu/cc at room temperature. Thermally activated charge transport dominated via oxygen vacancies as calculated by their activation energy, which was consistent with current–voltage characteristics. Magnetic field induced large change in resistance and capacitance of grain, and grain boundary was modeled by combined impedance and modulus spectroscopy in the presence of varied magnetic fields. Presence of large intrinsic magnetoelectric coupling was established by a maximum 20% increase in grain capacitance (Cg) with applied magnetic field (2 kG) on trilayer having 20 nm BiFeO3 layer. Substantially higher magnetoelectric coupling in thinner films has been observed due to bonding between Fe and Ti atoms at interface via oxygen atoms. Room temperature magnetoelectric coupling was confirmed by dynamic magnetoelectric coupling, and maximum longitudinal magnetoelectric coupling of 515 mV/cm-Oe was observed at 20 nm thickness of BiFeO3. The observed magnetoelectric properties are potentially useful for novel room temperature magnetoelectric and spintronic device applications for obtaining higher voltage at lower applied magnetic field.

Multi-bits memory cell using degenerated magnetic states in a synthetic antiferromagnetic reference layer

We newly developed a magnetic memory cell having multi-bit function. The memory cell composed of a perpendicularly magnetized magnetic tunnel junction (MB-pMTJ) and a synthetic antiferromagnetic reference layer. The multi-bit function is realized by combining the freedom of states of the magnetic free layer and that in the antiferromagnetically coupled reference layer. The structure of the reference layer is (FeB/Ta/[Co/Pt]3)/Ru/([Co/Pt]6); the top and the bottom layers are coupled through Ru layer where the reference layer has two degrees of freedom of a head-to-head and a bottom-to-bottom magnetic configuration. A four-state memory cell is realized by combination of both degrees of freedom.The states in the reference layer however is hardly detected by the total resistance of MB-pMTJ, because the magnetoresistance effect in the reference layer is negligibly small. That implies that the resistance values for the different states in the reference layer are degenerated. On the other hand, the two different states in the reference layer bring different stray fields to the free layer, which generate two different minor loop with different switching fields.Therefore, the magnetic states in the reference layer can be differentiated by the two-step reading, before and after applying the appropriately pulsed magnetic field which can identify the initial state in the reference layer. This method is similar to distinguishing different magnetic states in an in-plane magnetized spin-valve element. We demonstrated that four different states in the MB-pMTJ can be distinguished by the two-step read-out. The important feature of the two-step reading is a practically large operation margins (large resistance change in reading) which is equal to that of a single MTJ. Even though the two-step reading is a destructive method by which 50% of the magnetic state is changed, this MB-pMTJ is promising for high density non-volatile memory cell with a minor cost of operation speed.

Nearly isotropic piezoresistive response due to charge detour conduction in nanoparticle thin films.

Piezoresistive responses of nanoparticle thin-film strain sensors on flexible polyimide substrates were studied. Disordered interparticle tunneling introduces microscopic detour of charge conduction so as to reduce gauge factors. The disorder also results in large resistance change when current flows in the direction perpendicular to a unidirectional strain, reducing response anisotropy. For practical usages, stability and endurance of these strain sensors are confirmed with 7 × 104 bending cycles. Cracks form in devices under prolonged cyclic bending and slightly reduce gauge factor.

Asymmetrical multiphase front propagation and localized oscillations in a reaction-migration iron electrodissolution model with microfluidic flow cell geometry

We study nonlinear patterns in a reaction-migration system in microfluidic flow cell geometry with potentiostatic metal electrodissolution by using one- and two-variable electrode kinetics to model bistable, excitable, and oscillatory dynamics. On long electrodes in flow channel geometry, which is often used in lab-on-chip devices, the propagation of activity front (in the bistable region) was found to be a strongly asymmetrical, complex, multiphase process, with the onset of spontaneous secondary inactivation waves. On segmented electrodes, because of strong coupling, the activation front can hop over insulating segments. A common feature of bistable and excitable dynamics is that the front initiation from the remote (high resistance) edge is easier (requires less perturbation) compared to the close (low resistance) edge. In the oscillatory region, we found spatially localized oscillations located on the close part of the electrode, with oscillation properties depending on cell geometry parameters. The flow cell geometry induces large changes in the local resistance along the electrodes in the flow channel, especially between the remote and close edges; this variation creates largely heterogeneous dynamical units, whose coupling accounts for many features of the observed complex behavior.

Native Defects And Optical Properties Of Ar Ion Irradiated ZnO

MeV Argon (Ar) ion irradiation turns white coloured ZnO to yellowish (fluence 1 × 10 14 ions/cm 2 ) and then reddish brown (1 × 10 16 ions/cm 2 ). At the same time the material becomes much more conducting and purely blue luminescent for the highest fluence of irradiation. To get insight on the defects in the irradiated samples Ultraviolet-visible (UV-vis) absorption, Raman, and photoluminescence (PL) spectroscopy and Glancing Angle X-Ray Diffraction (GAXRD) measurements have been carried out. Enhancement of overall disorder in the irradiated samples is reflected from the GAXRD peak broadening. UV-vis absorption spectra of the samples shows new absorption bands due to irradiation. Complete absorption in the blue region of the spectrum and partial absorption in the green and red region changes the sample colour from white to reddish brown. The Raman peak representing wurtzite structure of the ZnO material (~ 437 cm -1 ) has decreased monotonically with the increase of irradiation fluence. At the same time, evolution of the 575 cm -1 Raman mode in the irradiated samples shows the increase of oxygen deficient disorder like zinc interstitials (IZn) and/or oxygen vacancies (VO) in ZnO. PL spectrum of the yellow coloured sample shows large reduction of overall luminescence compared to the unirradiated one. Further increase of fluence causes an increase of luminescence in the blue region of the spectrum. The blue-violet emission can be associated with the interstitial Zn (IZn) related optical transition. The results altogether indicates IZn type defects in the highest fluence irradiated sample. Large changes in the electrical resistance and luminescent features of ZnO using Ar ion beam provides a purposeful way to tune the optoelectronic properties of ZnO based devices. Copyright © 2015 VBRI press.

Soft metal constructs for large strain sensor membrane

Thin gold films on silicone display large reversible change in electrical resistance upon stretching. Eutectic liquid metal conductors maintain bulk metal conductivity, even upon extensive elongation. When integrated together, the soft metals enable multidirectional, large strain sensor skin. Their fabrication process combines thermal evaporation of thin gold film patterns through stencil mask with microplotting of eutectic gallium indium microwires, and packaging in silicone rubber. Using three-element rectangular rosettes, we demonstrate a sensor skin that can reliably and locally quantify the plane strain vector in surfaces subject to stretch (up to 50% strain) and indentation. This hybrid technology will find applications in soft robotics, prosthetics and wearable health monitoring systems.

Bulk ZnO as piezotronic pressure sensor

The impact of uniaxial compressive mechanical stress on the electrical properties of a ZnO varistor ceramic was studied with respect to a potential use in pressure sensor applications. Current-voltage measurements as a function of temperature are strongly affected by the applied stress. The modulation of charge transport properties with uniaxial stress causes large changes in resistance. Hence, a gauge factor of ∼800 is attained, which significantly exceeds the value of conventional sensors. The effect is attributed to the piezotronic effect, i.e., the altering of the potential barrier at grain boundaries due to the piezoelectricity of ZnO. This change in grain boundary potential barriers via mechanical deformation represents a promising physical concept for the development of better materials for sensor applications.

Observation of negative magneto-resistance in SrFe1−xTixO3−δ (x = 0 to 0.3) systems

Resistance and magneto-resistance of nanocrystalline SrFe1−xTixO3−δ (x = 0 to 0.3) systems are investigated. Substitution of non magnetic Ti4+ stabilizes the single phase tetragonal crystal structure with I4/mmm space group and Ti introduces bond disorder as well as site disorder. With increase in Ti content, the disorder increase leading to localization and large change in resistivity is observed in all the systems. In undoped system, the increase in resistivity is associated with the magnetic transition. All the Ti doped samples show large change in resistivity much above the magnetic ordering temperature and three dimensional Variable Range Hopping mechanism seems to explain the transport and magneto-transport behavior in these systems.

Giant Magnetoresistance and Oscillations In Interlayer Exchange Coupling In Co/Cu/Co Multi-Layers

The oscillations in interlayer exchange coupling between ferromagnetic layers which are Separated by a nonmagnetic spacer layer, manifests n oscillatory magnetic properties which depend on the thickness of Copper interlayer. Using Molecular Beam Epitaxy system. We have made multilayer films with alternating cobalt and copper thin films. The preliminary results are reported on microstructure and magnetization properties. The conductance between first and third film depends on the relative orientation of magnetization between them. This optimizes to large magneto resistance changes called Giant Magneto-resistance effect.

Mechanism for the large conductance modulation in electrolyte-gated thin gold films

Electrolyte gating using ionic liquid electrolytes has recently generated considerable interest as a method to achieve large carrier density modulations in a variety of materials. In noble metal thin films, electrolyte gating results in large changes in sheet resistance. The widely accepted mechanism for these changes is the formation of an electric double layer with a charged layer of ions in the liquid and accumulation or depletion of carriers in the thin film. We report here a different mechanism. In particular, we show using x-ray absorption near edge structure (XANES) that the previously reported large conductance modulation in gold films is due to reversible oxidation and reduction of the surface rather than the charging of an electric double layer. We show that the double layer capacitance accounts for less than 10\% of the observed change in transport properties. These results represent a significant step towards understanding the mechanisms involved in electrolyte gating.

콘크리트내로 침투하는 염소이온 반응형 부식센서의 응답특성에 미치는 센서 세선 수의 영향에 관한 실험적 연구

본 연구에서는 콘크리트내로 침투하는 염소이온을 모니터링하기 위하여, 스크린프리트 기법으로 염소이온 반응형 부식센서를 개발하고, 센서의 세선 수가 부식반응도 및 민감도에 미치는 영향을 실험을 통하여 정량적으로 분석하였다. 개발된 부식센서를 이용하여 염소이온량에 따라 부식 반응도을 확인하였으며, 센서의 파괴정도에 따른 저항변화에서는 단선형 센서보다 다선형 센서에서 큰 저항 변화를 나타내었다. 또한, 부식센서는 NaCl 수용액의 농도가 높은 만큼 센서의 저항변화가 크고, 콘크리트 내에서 센서 종류에 따른 부식저항은 단선형보다 다선형에서 민감도가 높게 나타났으며, 센서의 매설깊이가 클수록 저항변화 사이클 (cycle)은 증가하였다. 이상의 결과로, 본 연구에서 개발된 부식센서는 염분에 대한 부식반응과 민감도, 저항의 변화를 감지할 수 있었으며, 특히 7세선이 우수한 결과를 나타내어, 염분의 침투정도를 모니터링 하는데 가장 적합하다고 판단된다. In this study, the sensor response and sensitivity is experimented and analyzed quantitatively by the line numbers of chlorine ion reaction type corrosion sensor that is developed. The sensor response of the developed corrosion sensor is verified with properties of chlorine ion. The multilineal sensor is shown a large resistance change more than the single line sensor by damage of the sensor. And, the resistance change of sensor is as large as high concentration of NaCl aqueous solution, the sensitivity of multilineal sensor is higher than single line sensor's, and the depth of sensor's location is as large as the increasing of resistance change time (cycle). These results suggest that, the developed corrosion sensor could sense corrosion reaction, sensor sensitivity and change of resistance for chloride ion. Especially, It was judged that 7 line sensor was the most superior for monitoring chloride ion immigration into concrete.